How many cells are in the human body?
A careful 2016 recount put the reference adult male at about 30 trillion human cells and roughly 38 trillion bacteria — a ratio of about 1.3 to 1, not the 10 to 1 that textbooks repeated for forty years. The old ratio traced to a single 1972 back-of-envelope estimate that was never checked. The composition is also surprising: about 84% of human cells by number are red blood cells, which are tiny and have no nucleus, while the cells that make up most of the body's mass — muscle and fat — are a rounding error by count.
How the figure is arrived at
Organ by organ, rather than dividing body mass by an average cell size. For each tissue, take its mass and divide by the measured mass of a typical cell of that type, using histology data. That approach is what exposed the error: red blood cells dominate any count, and any method that ignores cell-type differences gets the answer badly wrong.
How confident it is
- Low estimate
- 25,000,000,000,000
- High estimate
- 35,000,000,000,000
- Spread
- 1.4× between the bounds
Other the human body counts
- How many bones are in the human body? 206 in an adult — about 300 at birth
- How many neurons are in the human brain? about 86 billion
- How many muscles are in the human body? about 600 skeletal muscles
- How many hairs are on your head? about 100,000
- How many taste buds do you have? about 2,000 to 8,000
- How long are all your blood vessels? commonly quoted as 100,000 km — but probably closer to 20,000
- How many base pairs are in human DNA? about 3.1 billion per copy — 6.2 billion in most cells
Common questions
- How many cells are in the human body?
- about 30 trillion human cells, plus 38 trillion bacteria
- How is that estimated?
- Organ by organ, rather than dividing body mass by an average cell size. For each tissue, take its mass and divide by the measured mass of a typical cell of that type, using histology data. That approach is what exposed the error: red blood cells dominate any count, and any method that ignores cell-type differences gets the answer badly wrong.
Related pages
- How many bones are in the human body? 206 in an adult — about 300 at birth
- How many neurons are in the human brain? about 86 billion
- How many muscles are in the human body? about 600 skeletal muscles
- How many hairs are on your head? about 100,000
- How many taste buds do you have? about 2,000 to 8,000
- How long are all your blood vessels? commonly quoted as 100,000 km — but probably closer to 20,000
- How many base pairs are in human DNA? about 3.1 billion per copy — 6.2 billion in most cells
- How many people are there in the world? Living things and the natural world
- How many stars are there in the universe? Space and the universe
- How many countries are there in the world? Things people built
- How many grains of sand are there on Earth? Living things and the natural world
- How many ants are there in the world? Living things and the natural world
- How many trees are there in the world? Living things and the natural world
Sources
- Typical range compiled from manufacturer specifications — At One Place